1. Field of the Invention
The present invention relates to flame-retardant thermoplastic resin compositions. More particularly, the present invention relates to the thermoplastic resin compositions which comprise a polycarbonate, a styrene containing graft copolymer, a styrene containing copolymer, a mixture of alkyl substituted, preferably t-butyl substituted, monophosphate esters, a phosphate ester compound, and a fluorinated polyolefin, whose stress cracking resistance and flame retardancy are improved.
2. Discussion of Related Art
Polycarbonate resin compositions are widely used for parts of electrical products and automotive-components because they have a good combination of transparency, high impact strength, and heat resistance. But, polycarbonate resin compositions have poor ocessability during molding process, so polycarbonate resin compositions are usually blended with other resins for improving these properties. For example, a molding composition comprising a polycarbonate resin and a styrenic resin has good processability as well as high notched impact strength.
Furthermore, the polycarbonate molding composition used for parts of home and office appliances should be flame resistant to prevent fires.
To confer flame retardancy to thermoplastic molding compositions, halogen and/or antimony containing-compounds have been incorporated. In U.S. Pat. Nos. 4,983,658 and 4,883,835, a halogen-containing compound is used as a flame retardant. The halogen-containing compound, however, results in corrosion of the mold itself by the hydrogen halide gases released during a molding process and is fatally harmful due to the toxic gases liberated in the case of fire.
As a method for conferring flame-retardancy without using a halogen-based flame retardant, a method using a phosphate ester-based flame retardant is commonly used. The use of halogen-free phosphate ester compound as flame retardants avoids the problems caused by the corrosive and harmful by-products of halogen-based flame retardants. However, the phosphate ester-based flame retardants have tendency to cause deterioration of heat resistance, occurring of stress crack by volatilization of a flame retardant, and juicing during a molding process.
As a method for overcoming these problems, Japanese Patent Publication No. (Sho)62-25706 describes the use of a mixture of an arylphosphate ester prepared by reacting a phosphorus oxychloride with a divalent phenol and a monovalent phenol, and an oligomeric phosphate ester as a flame retardant. However, in this method, the flame retardant prepared by such method results in the corrosion of the mold itself by a phosphorus oxychloride and a residual metal ion derived from a metal salt used as a catalyst such as aluminum chlorides, magnesium chlorides, and so on.
U.S. Pat. Nos. 5,061,745 and 5,030,675 describe polymer blends prepared from an aromatic polycarbonate, an ABS graft copolymer, a styrene containing copolymer, a monophosphate ester such as triphenylphosphate(TPP) as flame retardants, and a fluorinated polyolefin. However, the low stress cracking resistance of these molding compositions often restricts the application of non-halogen-PC/ABS in the field of making parts of electronic and electric products, especially thin-walled parts. And heat resistance of these blends also deteriorates substantially.
In order to reduce the occurrence of stress cracking and deterioration of heat resistance by the use of a monophosphate ester, U.S. Pat. No. 5,204,394 describes a polymer mixture comprising an aromatic polycarbonate, a styrene containing copolymer and/or a styrene containing graft copolymer and an oligomeric phosphate as a flame retardant. In this polymer mixture, it is possible to obtain a V-O rating according to UL-94 using by the oligomeric phosphate whose condensation degree is about 1.4. However, if the condensation degree of the oligomeric phosphates exceed 2.8, the flame retardancy of this polymer mixture decreases rapidly to HE rating and stress cracking resistance of the mixture also decreases.
U.S. Pat. No. 5,672,645 describes flame retardant polycarbonate/ABS molding compounds whose stress cracking resistance is improved by a combination of additives comprising a monomeric phosphorus compound and an oligomeric phosphorus compound as compared with the molding compounds comprising only a monophosphorus compound or an oligomeric phosphorus compound, respectively. However, the heat resistance and stress cracking resistance of these compounds are not sufficient, so an improvement is required.
U.S. Pat. No. 5,206,404 describes compositions of alkylated triphenyl phosphate esters comprising 1 to 20% by weight trialkylphenyl phosphate, 10 to 50% by, weight dialkylphenyl monophenyl phosphate, 15 to 60% by weight monoalkylphenyl diphenyl phosphate and less than 2% by weight triphenyl phosphate. However, this publication contains no indication of any improvement in stress cracking resistance and flame retardancy of thermoplastic resin compositions by adding these mixtures of triaryl phosphate esters.
The present invention is based on the discovery that flame retardant thermoplastic resin compositions with excellent stress cracking resistance and heat-resistance may be produced by adding flame retardants comprising a phosphate ester and a mixture of alkyl substituted, preferably t-butyl substituted, monophosphate esters of U.S. Pat. No. 5,206,404. The flame retardant thermoplastic resin compositions of this invention have good stress cracking resistance and elevated heat resistancy as compared with the molding compound of U.S. Pat. No. 5,672,645 comprising a monophosphorus compound and an oligomeric phosphorus compound as a flame retardant.
An object of the present invention is to provide a flame-retardant thermoplastic resin composition with excellent stress cracking resistance and improved heat resistance which comprises a polycarbonate, a styrene containing graft copolymer, a styrene containing copolymer, a mixture of alkyl substituted, preferably t-butyl substituted, monophosphate esters, a phosphate ester, and a fluorinated polyolefin.
The present invention relates to thermoplastic resin compositions comprising:
(A) 40 to 95 parts by weight of a halogen-free, thermoplastic polycarbonate;
(B) 5 to 50 parts by weight of a styrene containing graft copolymer prepared by grafting (B-1) onto (B-2)
(B-1) 5 to 95% by weight, based on (B), of a mixture of
(B-1.1) 50 to 100% by weight of styrene, xcex1-methyl styrene, nucleus-substituted styrene, methyl methacrylate or a mixture thereof, and
(B-1.2) 50 to 0% by weight of acrylonitrile, methacrylonitrile, C1-C8 alkyl methacrylate, C1-C8 alkyl acrylate, maleic anhydride, N-substituted maleimide, or a mixture thereof
(B.2) 95 to 5% by weight, based on (B), of a rubber with a glass transition temperature(Tg) of below xe2x88x9210xc2x0 C. and selected from the group consisting of butadiene rubbers, acryl rubbers, ethylene/propylene rubbers, styrene/butadiene rubbers, acrylonitrile/butadiene rubbers, butadiene/styrene rubbers, polyisoprene, EPDM (ethylene-propylene-diene terpolyrner) rubbers, polyorganosyloxane, and mixtures thereof;
(C) 0 to 30 parts by weight of a styrene containing copolymer prepared from
(C-1) 50 to 95% by weight of styrene, xcex1-methyl styrene, nucleus-substituted styrene, methyl methacrylate or a mixture thereof, and
(C-2) 50 to 5% by weight of acrylonitrile, C1-C8 alkyl methacrylate, C1-C8 alkyl acrylate, or a mixture thereof,
(D) 5 to 20 parts by weight, based on 100 parts by weight of (A)+(B)+(C), of a mixture comprising
(D-1) 100 to 5% by weight of admixture of alkyl substituted, monophosphate esters of the formula(I) 
xe2x80x83in which,
R is an alkyl group selected from t-butyl, isopropyl, isobutyl, isoamyl, t-amyl and N is 0 or an integer from 1 to 3, and
(D-2) 0 to 95% by weight of phosphate esters of the formula (II) 
xe2x80x83in which,
R1, R2, R4, and R5 are independently cresyl, phenyl, xylenyl, propylphenyl, butylphenyl, or brominated or chlorinated derivatives thereof,
R3 is an arylene group, and
M is 0 to 5; and
(E) 0 to 2 parts by weight, based on 100 parts by weight of (A)+(B)+(C), of a fluorinated polyolefin polymer.
In addition to the components mentioned hereinbefore, the thermoplastic resin compositions according to the present invention may further contain one or more conventional additives. For example, inorganic fillers such as mica, talc, zeolite, and montmorillonite, pigments, dyes, glass fibers, carbon fibers, thermal stabilizers, light stabilizers, antioxidants, plasticizers, and mold release agents may be added in fabrications as needed.
The thermoplastic resin compositions according to the invention comprise a polycarbonate, a styrene containing graft copolymer, a styrene containing copolymer, a mixture, of alkyl substituted monophosphate esters, a phosphate ester compound and a fluorinated polyolefin polymer.
Hereinafter the detailed description regarding the respective components is provided.
Suitable component (A) thermoplastic halogen-free polycarbonates according to the invention are those generally prepared by reacting diphenols of the following formula ( ) with a phosgene or a carbonic diester. 
in which,
A is a single bond, C1-C5 alkylene, C2-C5 alkylidene, C5-C6 cycloalkylidene, xe2x80x94Sxe2x80x94 or xe2x80x94SO2xe2x80x94.
Suitable diphenols of the formula (III) are, for example, 4,4xe2x80x2dihydroxydiphebnyl, 2,2-bis-(4-hydroxyphenyl) propane, 1,1-bis-(4-hydroxyphenyl) cyclohexane, and the like. The most preferred and widely used thermoplastic, halogen-free polycarbonates are aromatic polycarbonates synthesized from 2,2-bis(4-hydroxy-phenyl)propane, called xe2x80x9cBisphenol Axe2x80x9d.
The production of the polycarbonates of component (A) suitable for use in accordance with the invention is known from literature, for example U.S. Pat. No. 3,169,121, and may be carried out in a known manner from diphenols with phosgene using the phase interface process or with phosgene using the homogeneous phase process.
Preferred polycarbonates according to the present invention have an weight average molecular weights (Mw as measured for example by ultracentrifugation or by scattered light measurement) of from 10,000 to 500,000 and preferably from 18,000 to 300,000. Polycarbonates with a certain molecular weight may be obtained by using a monophenol such as phenol, paracresol, or paraisooctylphenol as chain terminator. The polycarbonates suitable for use in accordance with the invention include both homopolycarbonates and copolycarbonates.
In the present invention, the polycarbonate resins(A) comprise a base resin along with styrene containing graft copolymers and styrene containing copolymers.
Styrene containing graft copolymer which may be used according to the invention are those prepared by grafting constituent (B-1) onto (B-2):
(B-1) 5 to 95% by weight, based on (B), of a mixture of
(B-1.1) 50 to 100% by weight of styrene, xcex1-methyl styrene, nucleus-substituted styrene, methyl methacrylate or a mixture thereof and
(B-1.2) 50 to 0% by weight of acrylonitrile, methacrylonitrile, C1-C8 alkyl methacrylate, C1-C8 alkyl acrylate, maleic anhydride, N-substituted maleimide or a mixture thereof
(B.2) 95 to 5% by weight, based on (B), of a rubber having a glass transition temperature(Tg) of below xe2x88x9210 and selected from the group consisting of butadiene rubbers, acryl rubbers, ethylene/propylene rubbers, styrene/butadiene rubbers, acrylonitrile/butadiene rubbers, butadiene/styrene rubbers, polyisoprene, EPDM rubbers, polyorganosyloxane, and mixtures thereof
Nucleus-substituted styrenes (B-1.1) are nucleus-alkylated styrenes such as, for example, p-methyl styrene. Particularly preferred styrene containing graft copolymer(B) is the so-called ABS resin.
The preferred average particle size of the rubber is from 0.05 to 4 in order to improve the impact strength and the appearance of the moldings.
The styrene containing graft copolymers of component (B) may be prepared according to conventional methods of preparing copolymer, in particular, emulsion, suspension, solution or bulk polymerization. Preferred method for preparing the graft copolymer (B) is emulsion or bulk process.
The styrene containing copolymers of component (C) to be used in accordance with the invention are those prepared from: (1) 50 to 95% by weight of styrene, -methyl styrene, nucleus-substituted styrene, methyl methacrylate or a mixture thereof(C-1), and (2) 50 to 5% by weight of acrylonitrile, C1-C8 alkyl methacrylate, C1-C8 alkyl acrylate, or a mixture thereof(C-2). A specific example of the styrene containing copolymer is SAN(styrene/acrylonitrile) resin, which is prepared by copolymerizing styrene and acrylonitrile. In the copolymerization, 60 to 90% by weight of styrene and 40 to 10% by weight of acrylonitrile are used.
The styrene containing copolymer of component (C) may be prepared by conventional copolymerization processes, in particular, by suspension or bulk polymerization.
(D-1) A Mixture of Alkyl Substituted Monophosphate Esters
The thermoplastic resin compositions according to the present invention contain as a flame retardant a mixture of alkyl substituted monophosphate esters(D-1), and a phosphate ester compound(D-2). Component (D-1) is a mixture of alkyl substituted monophosphate esters of the following formula (I) 
in which,
R is an alkyl group selected from t-butyl, isopropyl, isobutyl, isoamyl, t-amyl, and N is 0 or an integer from 1 to 3,
Preferrably, the component (D-1) is a mixture of alkyl substituted monophosphate esters comprising by weight 1 to 20% trialkylphenyl phosphate(N=3), 10 to 50% dialkylphenyl monophenyl phosphate(N=2), 15 to 60% monoalkylphenyl diphenyl phosphate(N=1) and less than 2% triphenyl phosphate(N=0). The preferred substituent R is t-butyl and isopropyl. The most preferred substituent R is t-butyl. A mixture of the mixed t-butylphenyl phosphate esters and the mixed isopropylphenyl phosphate esters are also preferrable.
(D-2) Phosphate Esters
The phosphate esters according to the invention have the following formula(II). 
in which,
R1, R2, R4, and R5 are independently halogen-free phenyl group or C1-C4 alkylated aryl group,
R3 is an arylene group, and
M is 0 to 5.
In the formula, the compound of which M is 0, is a usual monomeric phosphate ester and the compound of which M exceeds 0, is an oligomeric phosphate compound. That is, the phosphate-based flame retardant useful in the thermoplastic resin compositions according to the present invention comprises compounds of the formula (II) having M values from 0 to 5.
Preferred substituents R1, R2, R4, and R5 are independently one of cresyl, phenyl, xylenyl, propylphenyl, butylphenyl, and brominated or chlorinated derivatives thereof R3 is derived from diphenols such as, for example, bisphenol A, resorcinol or hydroquinone. Examples of preferred phosphate esters are a phosphate ester such as triphenyl phosphate, tri(2,6-dimethylphenyl) phosphate, tri(4-methylphenyl) phosphate, tricresyl phosphate, diphenylcresyl phosphate, tri(isopropylphenyl) phosphate, trixylenyl phosphate, xylenyldiphenylphosphate, an oligomeric phosphorus compound thereof, or mixtures of these compounds.
The thermoplastic resin compositions according to the invention contain a mixture of (D-1) and (D-2) as a flame retardant. The weight ratios of (D-1) and (D-2) may be varied within a wide range. The weight ratio of (D-1) to (D-2) is preferably between 100:0 and 5:95, more preferably between 80:20 and 5:95 and the most preferably between 55:45 and 15:85.
Preferred fluorinated polyolefins (E) are polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene/vinylidene fluoride copolymer, and tetrafluoroethylene/hexafluoropropylene copolyemer. These fluorinated polyolefins may be used alone or in admixture with other two or more fluorinated polyolefins. These polymers may be produced by known processes, such as for example, by polymerization of tetrafluoroethylene in an aqueous medium with a free radical forming catalyst.
The use of fluorinated polyolefins decreases flow viscosity of the thermoplastic resin composition and increases coefficient of shrinkage of the composition by forming a fibrillar network during extruding, thereby reducing or preventing the dripping of the melting resin.
The fluorinated polyolefins may be used in powder form or in emulsion form. Fluorinated polyolefins of emulsion form have good dispersibility, but make the preparation process complicated. Therefore, it is desired to use powder form fluorinated polyolefins capable of being dispersed evenly in the total resins and forming fibrillar network.
The fluorinated polyolefin suitable for use in accordance with the invention is polytetrafluoroethylene. Polytetrafluoroethylene with an average particle size of 0.05 to 1,000 xcexcm is suitable for blending.
0 to 2.0 parts by weight of a fluorinated polyolefin polymer, based on 100 parts by weight of the base resin (A)+(B)+(C) is blended.
In addition to the above-mentioned constituents, the thermoplastic resin compositions according to the invention may further contain one or more other conventional additives. For example, inorganic fillers, thermal stabilizers, antioxidants, light stabilizers, plasticizers, pigments, dyes, and mold releasing agents may be added. The content of these conventional additives may be 0 to 50 parts by weight based on 100 parts by weight of the base resin (A)+(B)+(C).
The thermoplastic resin compositions are prepared according to the conventional techniques of preparing resin compositions, for example, by mixing together the constituents including the various additives and melt-extruding with extruders in pellet form.
Following are examples which illustrate procedures including the best mode, for practicing the invention. They are not to be construed to limit the scope of the invention defined by the appended claims in any manner whatsoever. All percentages are by weight unless otherwise noted.
The following constituents were used in the examples hereinafter:
(A) Polycarbonate
Polycarbonate of Bisphenol A having a weight average molecular Weight of 20,000 was used.
(B) Styrene-containing Graft Copolymer (ABS)
45 parts by weight of butadiene latex in powder, 36 parts by weight of styrene, 14 parts by weight of acrylonitrile, and 150 parts by weight of deionized water were mixed, and 1.0 parts by weight of potassium oleate, 0.4 parts by weight of cumene hydroperoxide, and 0.3 parts by weight of mercaptan-based chain transfer agent were added to the mixed solution. The resulting solution was kept at 75xc2x0 C. for 5 hours to prepare a graft ABS(g-ABS) latex. To the resulting graft copolymer, 1% sulfuric acid solution was added to prepare ABS resin in powder.
(C) Styrene-containing Copolymer(SAN)
To a mixed solution of 70 parts by weight of styrene, 30 parts by weight of acrylonitrile and 120 parts by weight of deionized water, 0.2 parts by weight of azobisisobutylonitrile and 0.5 parts by weight of tricalcium phosphate were added. SAN copolymer was prepared by suspension polymerization by washing, dehydrating and drying the resultant product. SAN copolymer in powder form was obtained.
(D-1) A mixture of t-butyl substituted monophpsphate esters
A mixture of t-butyl substituted monophosphate esters containing 0.5% by weight of triphenyl phosphate, 33.2% by weight of diphenyl (t-butylphenyl) phosphate, 49.5% by weight of phenyl di(t-butylphenyl) phosphate and 12.5% by weight of tri(t-butylphenyl) phosphate was used.
(D-2 1) Monomeric phosphate ester
Triphenyl phosphate (TPP) of Daihachi Co. of Japan was used.
(D-22) Oligomeric phosphate ester
Resorcinoldiphosphate(RDP) with and average M value of 1.3 in Formula (II) was used.
(E) Fluorinated polyolefin
Polytertrafluoroethylene with an average particle size of 10-50 xcexcm was used.